Hub for magnetic tape cassettes, especially compact cassettes, and magnetic tape cassette possessing one or more such hubs

ABSTRACT

The invention relates to a hub for magnetic tape cassettes, especially compact cassettes, and to magnetic tape cassettes possessing such hubs. In a first embodiment, spring means are provided on the inner periphery of the hub and exert radial pressures on the drive spindle, the spring means consisting, for example, of sprung teeth. In a further embodiment, the teeth have a spring rate of from about 1 P/mm to 40 P/mm. In another embodiment, the hub consists of an inner part and an outer part which can be coupled to one another and between which there is some play after coupling. A large number of specific examples of hubs are given to show possible shapes and arrangements of the teeth, and to show the types of material that can be used. In an advantageous embodiment, the inner part of the two-part hub can also be made a part of the drive spindle on the recorder, which inner part can be coupled with the outer part when the drive spindle enters the cassette.

The present invention relates to a hub for magnetic tape cassettes,especially compact cassettes, comprising a ring member, on whose innerperiphery teeth are provided for cooperation with the drive spindle,having projecting keys, of the recorder, and to a magnetic tape cassettehaving at least one such hub.

Though the distances between mutually opposite teeth on the hub of acassette are standardized, excessive play between the teeth and thedrive spindle is found, in particular due to the manufacturingtolerances of the recorder. In cassette recorders in which the cassettesare operated horizontally, but especially in recorders in which thecassettes are operated vertically, periodic, abrupt slipping of thereels in the cassette during recording and/or playback is observed, withperceptible fluctuations in pitch.

German Laid-Open Application DOS No. 1,946,536 has disclosed, for filmcassettes, a film reverse drive--to make it possible to producedissolving effects--in which a greater frictional torque is exerted thanin the forward mode. In the conventional super-eight film cassettehaving one reel, the reel is provided, on the inner periphery with twosprung friction tabs which cooperate with the drive shaft to producebraking forces which differ from one another depending on the directionof transportation. The surface structure of the tab which in each caseinteracts with the drive shaft serves to create the differing brakingforces.

In this known arrangement, not only is the drive shaft/reel driveconnection completely different from magnetic tape twin-reel cassettes,but so also is the object to be achieved.

German Utility Model No. 75/21,898 discloses the use, for hubs in audiotape cassettes, of spring-loaded braking members which, when thecassette is taken out of the recorder, bear against the serving collarsas bearings for the hubs, so that the hubs are locked and the formationof loops of tape inside the cassette is prevented. When the hubs arepushed onto the drive shafts of the recorder, the braking members areautomatically released. These known hubs have a completely differentpurpose from that of the present invention.

Further, German Laid-Open Application DOS No. 2,056,932 discloses a tapecassette with tape rolls on hubs which are rotatable in ball bearings.In order to compensate for tolerances in the position and constructionof the drive spindles, the inner part of the hub is made large relativeto the spindle diameter, so that inclined positions of the spindle canbe tolerated. The tolerances between the hubs and the cassette walls aremade close, so that, in conjunction with complex tape guide means,contact of the tape roll surfaces with the cassette walls can beprevented. For compact cassettes, these measures are too expensive,since they are unsuitable for mass production.

In compact cassette systems, compatibility between the cassette and therecorder or, rather, its drive spindles is achieved by arranging for thehubs to have some play, in the radial and axial directions, relative tothe cassette housing (FIG. 12). According to DIN 45,516, the followingtolerances are provided:

play in the radial direction, min.: 1 mm, max.: 1.9 mm

play in the axial direction, max.: 1.3 mm.

Play in the radial direction of the hub, relative to the cassettehousing, has the following disadvantages:

On fast rewinding, the hubs knock against the housing or bearing collarson the housing, especially on the supply side, and cause a distinctlyaudible rattling noise.

When the cassette is operated in a vertical position in the recorder,the hub runs so jerkily on the bearing collar on the supply side thatrapid variations in tape tension result, which in turn lead tovariations in pitch.

Play in the axial direction allows the hub and the tape roll --if thereis also radial play--to assume an inclined position relative to thecassette bottom and top, i.e. to wobble. This can result in the tapebeing wound non-uniformly so that the tape roll has uneven lateralsurfaces, as a result of which the frictional moment increases greatly,and the cassette frequently even freezes up. In addition, when operationof the cassette is suddenly started or stopped, the tape can slip offthe roll and jam between the roll and the cassette housing.

It is an object of the present invention to eliminate the excessive playbetween the drive spindle and the hub by providing a new hubconstruction which can be manufactured easily and economically.

We have found that this object is achieved with a hub for magnetic tapecassettes, especially for compact cassettes, consisting of a ring memberon whose inner periphery there are arranged teeth for cooperation withprojecting keys on the drive spindle, wherein the inner periphery of thehub is provided with spring means which exert radial pressures on thedrive spindle so as to reduce the play between the hub and the drivespindle.

The effectiveness of the spring means is independent of the direction ofrotation of the drive spindle; the spring means also enable the hub andhence the entire tape roll to be centered relative to the axis ofrotation. As a result, the aforementioned fluctuations in pitch, alsoreferred to as wow, can be avoided.

It is a further object of the present invention to reduce the tolerancesof hubs in the cassette housing, so that there is improved contactbetween the hub and the drive spindle, and the requisite play betweenthe hub and the spindle is predominantly accounted for by the hub.

We have found that this object is achieved with a hub for magnetic tapecassettes, especially for compact cassettes, consisting of a ring memberon whose inner periphery there are provided teeth for cooperation withprojecting keys on the drive spindle, wherein the hub consists of notless than two parts, which can be coupled with one another and betweenwhich there is play after coupling.

Accordingly, the invention relates not only to the hubs themselves butalso to the use of such hubs in cassettes, especially in compactcassettes, so that a tape cassette having such hubs itself alsoconstitutes an advantageous embodiment of the present invention.

Some magnetic tape cassettes according to the invention are definedbelow:

A magnetic tape cassette, especially a compact cassette, having at leastone hub consisting of a ring member, on whose inner periphery there arearranged teeth for cooperating with projecting keys on the drivespindle, conforms to the invention if the inner periphery of the hub isprovided with spring means which exert radial pressures on the drivespindle so as to reduce the play between the hub and the spindle.

The above cassette can also be provided, on the inner periphery of thehub, with one or more movable teeth which exert radial pressure on thedrive spindle of the recorder, so as to reduce the play between the huband the spindle, the spring rate of the movable tooth or teeth beingfrom about 1 P/mm to 40 P/mm.

A further advantageous magnetic tape cassette, especially a compactcassette, having at least one hub consisting of a ring member on whoseinner periphery there are provided teeth for cooperation with projectingkeys or the drive spindle of the recorder, there being only slight playbetween the inner walls of the cassette housing and the ring member,results if the hub consists of two parts, an inner part with teeth andan outer part, which parts can be coupled with one another for thetransmission of torque, a predetermined play being provided between theinner part and the outer part.

"Play", in the present context, is to be understood in the broader senseas meaning that relative movement between the inner part and the outerpart is possible. As a result, the outer part of the hub can beoptimally matched to the cassette housing, and just enough axial and/orradial play between the hub and the housing can be obtained, therequisite play for bringing about compatibility between the cassette andthe drive spindles of the recorder being obtained by the design of theinner part and the outer part of the hub, and by their relativearrangement.

Further feasible and advantageous embodiments of the hub according tothe invention include the following:

The teeth on the hub can be sprung relative to the ring member, so thatconstant contact with the drive spindle is achieved.

Advantageously, immovable teeth alternate with sprung teeth; inparticular, three of each are provided. The fixed teeth and sprung teethare arranged symmetrically with respect to the axis of rotation of thehub, as a result of which good centering of the hub is attainable.

In principle, the sprung teeth according to the invention can be movablein the horizontal plane of the hub or in a direction at right angles tothe hub. Which particular arrangement is preferred also depends on thedrive spindle of the recorder.

In a preferred embodiment of the invention, the sprung teeth arearranged symmetrically with respect to the axis of rotation of the huband there are not less than three such teeth.

In each case, the spring force, and the shape of the sprung teeth mustbe so chosen that insertion of the cassette into a recorder, andsubsequent removal of the cassette, can be effected without difficulty,regardless of the particular shape of the drive spindles or of anypossible axial play of the drive spindles.

In another advantageous practical embodiment at least one sprung toothhas a spring rate of from about 1 P/mm to 40 P/mm.

Independent movements of the hubs can be substantially avoided by meansof a frictional connection which is adequately guaranteed by the aboverange of spring rates. At the same time, it is ensured that the hubs caneasily be placed on, and coupled to, the drive spindles of the recorder,substantially independently of the particular dimensions of the spindleswhich, as experience shows, vary considerably between recorders fromdifferent manufacturers. In a further embodiment, the travel of anindividual sprung tooth or the total travel of diametrically opposedsprung teeth is from about 0.6 to 0.8 millimeter. In practice, it isadvantageous either to use four immovable and two sprung teeth or,conversely, four sprung and two immovable teeth.

Advantageously, the movable or sprung teeth have springs whoselongitudinal axis is in the horizontal plane of the hub.

It can assist manufacture to have the hubs constructed of two or moreparts, the immovable teeth being located on the rigid ring member andthe movable teeth on a movable, in particular a sprung, part. This makespossible separate manufacture of the respective parts, and enablesdifferent materials to be used.

In a further embodiment of the invention, one or more movable teeth canbe located on a part pivotable relative to the ring member, and therecan be several such pivotable parts. This makes it possible, if the ringmember is suitably cut away in the direction of rotation, to exertpressure on the drive spindle only when it rotates.

In an advantageous embodiment, two or more teeth can be provided on acommon support spring-loaded against the ring member. This simplifiesthe manufacture of the individual parts of the hub.

In a further embodiment, essentially only radial play is present betweenthe inner and outer parts of the hub. As a result, tolerances orinaccuracies of the drive spindles can be compensated.

In an advantageous embodiment, the inner and outer parts of the hub canbe of different materials, with the inner part preferably being made ofa resilient material and the outer part of a non-resilient material.This ensures that the inner part gives as the drive spindle enters orleaves it. It is even possible to fixedly mount such a resilient innerpart on the drive spindle provided steps are taken to ensure that as thedrive spindle enters the cassette the inner part comes into drivingconnection with the outer part of the hub, and comes out of engagementagain when the cassette is removed.

Further, the inner part can be designed as a clamping member for thedrive spindle, which improves power transmission when the spindlesrotate, and prevents undesired independent movements of the hub relativeto the drive spindle.

Further, it is possible to provide at least one spring element betweenthe inner part and the outer part, this element providing a resilientmounting of the inner part relative to the outer part and thusdetermining the magnitude of play.

In this way, the inner part and outer part can be resiliently coupledtogether. Advantageously, the spring element consists of elastomericfoam or sheet material, so that it can be manufactured economically.Finally, it is possible to arrange a plurality of spring elementssymmetrically with respect to the axis of rotation of the hub, or asingle spring element asymmetrically, on the hub, whereby either centricor eccentric mounting of the hub on the drive spindle is achievable.

Furthermore, the inner part and the outer part can be provided, on theouter periphery and the inner periphery respectively, with projectionsand corresponding recesses, so as to ensure a secure connection betweenthe inner part and outer part when the hubs rotate. Moreover, the innerpart can be designed as a clamping member for the annular collar on thecassette.

Details of the invention are disclosed below with reference to theembodiments shown in the accompanying drawings, in which

FIG. 1 shows a hub with three fixed teeth and three sprung teethattached to said fixed teeth,

FIG. 2 shows a hub with arcuate spring members for biassing the movableteeth;

FIG. 3 shows a hub with coil-spring-loaded teeth,

FIG. 4 shows a hub with leaf-spring-loaded teeth,

FIG. 5A is a diagram of the fluctuations in tape speed produced by aconventional hub, as a function of time.

FIG. 5B is a diagram of the fluctuations in tape speed produced by hubsaccording to the invention, as a function of time.

FIG. 6 shows a hub according to the invention, with asymmetricallyarranged movable teeth,

FIG. 6A shows a hub provided, at one side of the inner periphery, withtwo teeth on a sprung support,

FIG. 7 shows a hub with two symmetrically arranged spring support, eachhaving two teeth,

FIG. 8 shows a hub with four movable teeth, each attached to the ringmember via a leaf spring,

FIG. 9 shows a hub with two fixed teeth each having two sprung teethintegral therewith,

FIG. 10 shows a variant of the hub of FIG. 8, with four movable teeth,each fastened to the ring member via a leaf spring,

FIG. 11 shows a hub with movable teeth arranged on pivotally mountedmembers,

FIGS. 12A and 12B show a conventional one-part hub in a cassettehousing, with the drive spindle in engagement with the hub, A being aplan view with the cassette top removed, and B a section taken alongline a-b,

FIGS. 13A and 13B show a two-part hub according to the invention withthe drive spindle in engagement with the hub, A being a plan view withthe cassette top removed, and B a section taken along line a-b,

FIG. 14 shows a hub according to FIG. 13B, but with slight radial play,

FIG. 15B shows a slit inner part of a two-part hub, in plan view,

FIG. 15A shows a view, in section, of the inner part, in the lower partof the housing of the cassette,

FIG. 16 shows a two-part hub with an outer part asymmetrical to thehorizontal plane,

FIGS. 17A and 17B show two-part hubs with springy inserts between theinner part and the outer part, and

FIG. 18 shows a two-part hub, the inner part being integral with thedrive spindle.

FIG. 1 shows an annular hub 5, basically as used in compact cassettes.Additionally, spring means are provided so that three of the six teethnormally present are spring-mounted with respect to the ring member 7.In a conventional hub, all the teeth are integral with the ring member 7like the fixed teeth 8 in the Figure. In this special embodiment of thehub, a part of the inner periphery of the ring member 8 is undercut toform an arcuate groove 9, so that a springy member 10 bearing tooth 11is formed, the said tooth 11 thus being movable in the radial direction,as indicated in broken lines at 11a. The circle 12 described by the endsof the fixed teeth when the hub rotates is also shown in the drawing;the end 13 of the sprung tooth 11 projects beyond this circle by a smalldistance a. Normally this distance is a few tenths of a millimeter.However, suitable dimensions can be selected for each particular case.The arrangement of all the teeth 8 and 11 is symmetrical with respect tothe axis of rotation of the ring member 7, so that, in addition to areduction in play relative to the drive spindle (not shown) of therecorder, a centering action on the hub and hence on the entire tapereel is achieved. The sprung teeth of the hub may be of any size in theaxial direction, an upper limit being imposed by the spacing between thebearing collars on the cassette. The dimensions also depend on thematerial used, because adequate contact between the sprung teeth and thedrive spindle must be ensured, to allow the transmission of forces of asufficient magnitude which reliably hold the tape reel in an essentiallycentral position.

FIG. 2 shows a hub 12 whose inner peripheral surface is provided withsegment-shaped projections 14 which accommodate the fixed teeth 8 andsprung teeth 15. The sprung teeth 15 are fastened to the center ofarcuate springs 16. It is also conceivable to use these arcuate springs16 without the projections 14.

FIG. 3 shows a further hub 17 with fixed teeth 8 and sprung teeth 18,the teeth 18 being spring-loaded against the inner periphery of the ringmember 7 by means of coil springs 19, grooves 20 serving to guide theradial movements of the sprung teeth 18.

In a further embodiment (FIG. 4), a hub 21 having fixed teeth 8 andsprung teeth 22 is provided with horizontal flat leaf springs 23 whichallow the sprung teeth 22 also to move axially, which happens when thehub is placed on, and removed from, the drive spindle of the recorder.The spring force comes into effect as a result of the sprung teeth 22being deflected from the horizontal plane of symmetry. The front end 24of the sprung teeth 22 can have a domed shape, and this is also true inall the other embodiments.

The hubs are advantageously manufactured in one piece from a suitableplastic material by injection-molding. Of course, other processes, forexample compression-molding, can also be employed.

The force of the spring elements of the sprung teeth must be so adjustedthat the hub is held frictionally on the drive spindle. In principle,the number of sprung teeth can be chosen at will. It is advantageous tohave a sequence of alternating fixed teeth and sprung teeth, but anasymmetrical arrangement also has the above advantages of fixing thehub. In principle it is of course also possible to have, in addition tofixed teeth, spring members of any suitable shape on the ring member,without these spring members also having to be tooth-shaped.

FIG. 5A is the envelope of the measurements obtained with a cassettehaving conventional hubs in which all the teeth are fixed. FIG. 5B showsa similar envelope for a cassette with hubs according to FIG. 1. Theaverage wow G was about three times as great in the case of a cassettenot employing the hubs according to the invention.

As can also be seen from a comparison of envelopes 5A and 5B, FIG. 5Bessentially shows the wow attributable to the recorder, whilst FIG. 5Aessentially shows the wow attributable to the cassette. This latter wowis evidently caused by the additional independent movements of the hubsrelative to the drive spindles (i.e. by out-of-true running) and isvirtually completely eliminated by the invention.

The test apparatus and conditions were as follows:

Cassette recorder suitable for vertical operation: Sharp Optonica RT3838

Graphic recorder: Bruel and Kjaer level recorder, Model No. 2305,writing speed 63 mm/sec;

Wow and flutter meter: Woelke ME 105 (frequency at which measurementswere made: 3150 Hz (according to IEC (94), weighting filter switchedoff); and

The distance a (cf. FIG. 1)=about 0.15 mm.

FIG. 6 shows a hub, essentially of the conventional type, with fourfixed teeth 25. The fixed teeth 25 are rigidly attached to the ringmember 26 since the hub is a one-piece plastic injection molding.Opposite two of the fixed teeth 25 in the positions normally occupied byfixed teeth in the case of a conventional hub, there are provided sprungteeth, so that the arrangement of the sprung teeth 27 is unsymmetricalrelative to the horizontal center line. A drive spindle 28 is shown inengagement with the hub 30, the projections 29 on the spindle fittinginto the spaces between the teeth 25 and 27. The diameter of the drivespindle 28 is marked d_(D) and the diameter of the circle on which theend faces of the fixed teeth 25 lie is marked d. The sprung teeth 27project beyond the circle of diameter d by a distance Δd_(F) which isfrom about 0.3 to 0.4 mm when using approximately diametrically opposedsprung teeth 27. If only a single sprung tooth 27 is used, the distancehas to be doubled. Asymmetrical arrangements require a distance between0.3-0.8 mm.

Basically, the distance referred to is determined by the differentdiameters of the drive spindles of the recorders. A comparison of 17different recorders showed a difference between d_(D) min=7.35 mm andd_(D) max=7.65 mm of 0.3 mm. Since the DIN Standard specifies a diameterd of 7.8-8.0 mm for hubs, the play s which has to be compensatedaccording to the invention is --taking the minimum diameter d_(D) of thedrive spindle to be 7.35 mm--from 0.45 to 0.65 mm. With the additionalrequirement, according to the invention, that the spring force appliedby the sprung teeth should effectively act on the recorder drivespindle, and taking an average minimum spring travel of 0.15 mm, thetotal spring travel Δd_(F) is 0.6-0.8 mm.

Some further embodiments of hubs are described below.

In FIG. 6, the spring force can also be applied by sprung teeth 27 madeof a resilient, for example elastomeric or plastic foam, material andfixing them to the ring member 26 in a suitable manner, for example bygluing.

At the ends at which they are fixed, the sprung teeth 27 can also beprovided with plastic leaf springs or coil springs, provided that asubstantially radial spring action is desired.

FIG. 6A shows a hub 31, again with four fixed teeth 25 and two sprungteeth 32, but with the latter located on a flexible, bow-shaped support33. The support 33 can be closed or open at the rear, and isadvantageously fixed, at the rear, to the ring member 26. This againresults in a one-sided, unsymmetrical spring loading on the drivespindle 28. FIG. 6A shows a first embodiment of a two-part hub which,according to the invention, is of particular importance. Thus, theannular part 26 carrying the fixed teeth 25 can be produced in one piecefrom a rigid plastic, and the support 33 with the sprung teeth 32 can beproduced in one piece from a soft, resilient plastic, after which thetwo parts can be suitably joined, for example by a push-fit or snap-fitconnection or by gluing, ultrasonic welding, etc.

The spring rate of each sprung peg should be from about 1 P/mm to about40 P/mm (from 0.3 cN/0.3 mm to about 12 cN/0.3 mm), cN (Centinewton)being a hundredth of a Newton and P being a Pond. This spring rate isattainable with numerous plastics which are inherently springy orspringy by virtue of the particular shape, for example with almost allrubber or elastomeric materials, but also with thin flexible rigidplastics such as nylon, polypropylene and the like.

FIG. 7 shows a hub 34 with two diametrically opposed fixed teeth 25 andfour sprung teeth 35 arranged symmetrically with respect to the axis ofrotation of the hub 34, pairs of sprung teeth being located on a commonflexible support 36 which is fixed to the ring member at one end only.Since the support 36 increases in thickness and is fixed at one endonly, approximately the same spring force can be applied by each of thesprung teeth.

FIG. 8 shows a further embodiment in which hub 37 is provided with twodiametrically opposed fixed teeth 25 and four symmetrically arrangedsprung teeth 38. These teeth 38 are spring-loaded against the ringmember 26 by means of individual springs 39. These springs 39 can bethin, curved plastic elements which are integral with the teeth 38. Thesmaller the radius of the plastic springs, the less the effective springforce is. The sprung teeth 38 are bent toward the hub center. Recesses40 on the inner part of the ring member 26 serve to limit the travel ofthe sprung teeth. The teeth 38 can also be fastened separately tosprings 39. In an advantageous variant, an inner member 41 bearing thefixed teeth 25 and sprung teeth 38 is produced separately, and thismember is then fastened to the inside of the ring member 26.

FIG. 9 shows a hub 42 with two diametrically opposed fixed teeth 25, toeach of which two sprung teeth 43 are attached, or molded, via springelements 44. The inwardly curved spring elements 44 provide the springforce applied by the teeth 43. Fixed stops 45 limit the spring travel.

FIG. 10 shows, as a variant of the hub of FIG. 8, a hub 46 in which leafspring elements 47, bent back on themselves, and resembling those ofFIGS. 6A and 8, are used. Corresponding parts carry the same referencenumerals. In this embodiment and in the embodiment shown in FIG. 9, thehubs 42 and 46 can be manufactured in two or three parts, which isregarded as advantageous.

FIG. 11 shows a hub 48 with a ring member 26, approximately triangularcut-outs in the said ring member and triangular parts 50 pivotallymounted in the cut-outs 49. The cut-outs 49 are larger, in thecircumferential direction, than the pivoting parts 50. Two teeth 51 areprovided on each pivoting part 50. One of the pivoting parts 50 is shownin the deflected position resulting from rotation in the direction ofthe arrow a. The front sloping edge of the pivoting part 50 comes intocontact with the front wall of the cut-out, whilst the rear sloping edge52 lifts off from the rear sloping edge of the cut-out. As a result ofthis pivoting, the rear tooth 51 (viewed in the direction of the arrowa) projects beyond the circle of diameter d by an amount Δd_(F) and thusreduces the play relative to the drive spindle (not shown), whilstexerting a compressive force which depends on the speed of rotation. Thecut-out 49 and the pivoting part 50 are both of symmetrical shape, sothat a reduction in play results on rotation in either direction.

The pivoting parts 50 can be push-fit in the ring member 26. As a resultof the symmetrical arrangement of the three pivoting parts of identicalshape, the hub 48 is also centered relative to the drive spindle. Inprinciple, other shapes of the pivoting parts and of the correspondingcut-outs are also conceivable. Thus, for example, two pivoting partsarranged diametrically opposite one another also suffice to achievecentering.

Measurements carried out under conditions encountered in practice haveshown that the play between the hub and the drive spindle is greatlyreduced.

The results below were obtained on a Pioneer GT 700 cassette recorder,in vertical operation:

    ______________________________________                                        Hub play (mm)   Wow (%)                                                       ______________________________________                                        0.5             0.65                                                          0.2             0.40                                                          0.08            0.28                                                          0               0.26                                                          ______________________________________                                    

A comparison of the results shows that reducing the play, according tothe invention, from 0.5 mm to 0.08 mm more than halves the wow.

FIGS. 12A and 12B show views of a conventional hub 55, used in compactcassettes, in conjunction with a recorder drive spindle 61, havingprojecting ribs 71, in engagement with the hub. The cassette housing 81is shown in diagonal section through one of the orifices 91, thisorifice being defined by an annular collar 110a, 110b which projectssymmetrically with respect to the horizontal central plane of thehousing into the interior of the housing. The hub 55 is made in onepiece, in general from a plastic, and has, on its inner periphery, teeth111 which mesh with the projecting ribs 71 of the drive spindle 61 forrotation of the hub. The size of the circular cut-outs 112 determinesthe radial play rs=rs1+rs2 of the hub 52 relative to the annular collar110a, 110b. The axial play as is the sum of the component axial playsas1 and as2. Depending on their relative magnitudes, the axial play ofthe ring member 113 can additionally be determined by the axial play ksof the hub 55 between the opposite annular collars 110a and 110b.

As mentioned in the introduction, the amounts of the individual playsare as follows:

    1 mm≦rs≦1.9 mm and

    as≧1.3 mm.

The middle part 141 of the hub 55, which also carries the teeth 111 (ofwhich there are six in the example shown), rests on the lower annularcollar 110b. As a result, the axial plays as1 and as2 are unequal. Inthe ideal case, the hub 55, in operation on the recorder, is locatedprecisely in the middle of the housing 81, so that as1=as2.

FIGS. 13A and 13B show a first embodiment of a hub 151 according to theinvention, corresponding parts carrying the same reference numerals asin FIG. 12. The hub 15 consists of the inner part 116 and the outer part117, the inner part 116 being of a shape roughly corresponding to thatof the middle part 141 of the hub 55, and the shape of the outer part117 roughly corresponding to that of the ring member 113. The inner part116 and outer part 117 are connected or coupled to one another, orcapable of being connected or coupled to one another, by suitable means,in such a way that the torque produced by the drive spindle 61 engagingthe inner part 116 is transmitted to the outer part 117. As shown inFIG. 13A, the inner part 116 has, on its outer periphery, several--forexample three--projections 181, which engage recesses 119 on the innerperiphery of the outer part 117. The coupling between the inner part 116and outer part 117 can however also be achieved in any other suitablemanner. FIG. 13B shows that the radial play rk between the inner part116 and outer part 117 is special to this design, whilst the radial playrs is the same as in FIG. 12. However, the axial play as3 of the outerpart 117 relative to the housing 81 is substantially less, as a resultof which the advantages, mentioned above, of better and more accuraterotation of the reel are attainable. As a result of the special radialplay rk, tolerances attributable to the recorder and/or the cassette, ormechanical deficiencies of the recorder, for example skewing of thedrive spindle, incorrect location of the drive spindle, and variationsin diameter of drive spindles, can advantageously be compensated. In theaxial direction, the inner part 116 and outer part 117 are movablerelative to one another to any desired extent, as long as the plays areas in FIG. 13 and as long as there are no resilient members between theinner part 116 and outer part 117. The axial mobility of the inner part116 relative to the outer part 117 is restricted, in the embodimentshown, to the distance ks (cf. FIG. 12B) between the annular collars110a and 110b.

FIG. 14 shows a hub 120 wherein the play between the outer part 121 andthe annular collars 110a and 110b, i.e. in the radial direction, is muchless than in the case of the outer part 117 in FIG. 13. This reducedradial play rs3 has the advantage of even better centering andaccordingly of truer rotation of the hub 120 and thus also of the taperoll (not shown in the drawing). The inner part 122 corresponds to thepart 116 in FIG. 13, with a slightly smaller diameter. FIG. 15B shows aninner part 125 whose outer and inner diameters can be varied inaccordance with the particular width of the cut-out 124. A groove 123can be provided diametrically opposite the cut-out 124, if the materialof the inner part 125 is not inherently flexible enough. If theprojections 126 are of appropriate size, it is possible to clamp theinner part 125 over the annular collar 110b (cf. FIG. 15A) so that onlywhen the drive spindle 61 enters the inner part 125 is it released fromthe annular collar 110b, brought into the central position in thecassette housing, and there coupled to the corresponding outer part, notshown in the drawing. In any case, the projections 126 should be of sucha size relative to the recesses in the outer part that for any diameterof the inner part 125 the outer part of the hub is satisfactorily drivenby the inner part.

With this type of flexible inner part 125, it is particularly easy tocompensate diameter variations of drive spindles, so as to achieveoptimal centering. A series of measurements carried out on 17 differentcassette recorders showed that the drive spindles varied in diameterfrom 7.35 mm to 8.0 mm. It is, furtheremore, also possible to employteeth 111 of different length; for example, teeth 111a and 111b are at adistance from one another corresponding to the minimum diameter of 7.35mm, whilst the other teeth 111 are at a distance from one anothercorresponding to the maximum diameter of 8.0 mm, or vice versa. It ishowever advisable that any two diametrically opposed should be of equallength.

FIG. 16 shows an unsymmetrical hub 128, in contrast to the hubs hithertodescribed which are symmetrical with respect to the central plane of thecassette. The difference is to be seen essentially in the outer part127, which, compared to the outer part 121 in FIG. 14, has a cut-out136, corresponding to the cut-out bearing reference numeral 112 in FIG.12B, but in the present embodiment only associated with the upperannular collar 110a. There is only slight play between the lower half ofthe outer part 127 and the annular collar 110b, as in the case of theouter part 121 in FIG. 14. This design has the advantage that the hub128 is oriented only relative to one half of the housing, in the presentcase the lower part carrying the annular collar 110b; otherwise, thetolerances of the upper and lower parts of the housing have to be takeninto consideration in deciding the size of the hub.

FIG. 17A shows a hub 130 consisting of an inner part 122 and an outerpart 121, as in FIG. 13A, but here pieces of a resilient material, forexample an elastomeric foam, are provided in the gaps between theprojections 181 and the recesses 119. If three identical pieces of foam,129, are used, automatic centering of the inner part 122 is achieved. Ifonly one piece 129 is used, or if pieces having different resilience areused, it is possible to achieve a deliberate decentering of the innerpart 122, so that, for example, one or two of the ribs 71 on the drivespindle 61 come into contact with the teeth 111. FIG. 17B shows the samehub 130, but with pieces of springy sheeting 131 instead of the foampieces 129.

In both cases, a resilient coupling between the inner part 122 and outerpart 121 is desired, and the spring elements 129 and 131 are made fromappropriate materials and with appropriate dimensions.

FIG. 18 shows, as a further variant, a hub 135. As can be discerned inthe Figure, an inner part, essentially corresponding to the inner part125 in FIG. 15, is fixed on the drive spindle 61. The drivespindle/inner part assembly 132 thus enters the cassette orifice 91 asan entity and comes into engagement with the outer part 133, located inthe cassette housing 81; this outer part essentially corresponds to theouter parts 117 and 121 and can, if necessary, have resilient pieces offoam or sheeting, 129 or 131.

The coupling between a drive spindle/inner part assembly and an outerpart in the cassette can be effected in any appropriate manner which hasthe end result that the drive torque is transmitted substantiallywithout slip to the outer part and accordingly to the tape reel. Thus,for example, the inner and outer parts may be conical and may beprovided with an appropriate material which assists grip, but alsopermits easy separation of the parts.

Through appropriate choice of the material of the inner part and theouter part, with or without an intermediate part, it is possible toobtain the desired coupling forces between the inner part and outer partwhen the hubs are rotated. However, the outer part should besufficiently rigid to ensure that it can properly perform its functionof carrying the tape roll. Resilient materials can be used for the innerpart, provided the torque is nevertheless transmitted to the outer partessentially without loss. Care must be taken to ensure that thetolerances rs and as of the outer part relative to the cassette housingare not made too small as a result of the use of resilient materials forthe inner part of the intermediate part.

As regards the order of magnitude of the radial play and the axial playof the outer part relative to the housing, values of the order of 0.1mm≦rs, and as≦0.2 mm, are feasible in practice.

In practice, the play rk between the inner part and outer part of thehub is of the same order of magnitude as rs (see above).

In tests carried out under field operating conditions, it was found thatboth the mechanical and the electro-acoustic properties of commercialcompact cassettes were substantially improved by fitting the cassetteswith hubs designed according to the invention. By making the inner parta component of the recorder, i.e. by providing the drive spindle withthe part cooperating with the hub (outer part) in the cassette, it ispossible to reduce the cost of the cassette and improve the transmissionof torque from the drive spindle to the hub.

A resilient coupling between the inner part and outer part can beachieved by, for example, using an elastomeric adhesive.

In the last few embodiments mentioned, the requisite play isadvantageously provided, according to the invention, between the innerpart and outer part of the hub, so that very small play between theouter part and the cassette housing is achieved without there being anyneed to modify the housing.

We claim:
 1. A hub for magnetic tape cassettes, especially for compactcassettes, for use with a transport apparatus having a drive spindleprovided with projecting keys, said hub being displaceable in saidcassette in at least the radial direction, and comprising a ring memberon whose inner periphery there are arranged teeth for driving engagementby said projecting keys on the drive spindle,wherein said teeth include,in circumferentially spaced relation, a plurality of immovable teethwhich are radially spaced from the spindle, and also, in the same planewith said immovable teeth, at least one movable tooth which isspring-biased against the ring member to exert radial pressure on thedrive spindle, so as to resiliently couple said hub to said spindle andthereby counteract abrupt displacements of the hub relatively to thecassette and hence reduce corresponding fluctuations in pitch during theoperation of the cassette.
 2. A hub as claimed in claim 1, wherein saidat least one spring-biased tooth has a spring rate of from about 1 P/mmto 40 P/mm.
 3. A hub as claimed in claim 1, wherein immovable teethalternate with spring-biased teeth.
 4. A hub as claimed in claim 1,wherein four immovable teeth and two spring-biased teeth are provided.5. A hub as claimed in claim 1, wherein two immovable teeth and fourmovable spring-biased teeth are provided.
 6. A hub as claimed in claim1, wherein the spring-biased tooth possesses a spring which is effectivein the horizontal plane of the hub.
 7. A hub as claimed in claim 1,wherein the spring-biased tooth possesses a spring which is effective inthe axial direction of the hub.
 8. A hub as claimed in claim 1, whereinthe spring-biased teeth are arranged symmetrically with respect to theaxis of rotation of the hub and there are not less than three suchteeth.
 9. A hub as claimed in claim 1, wherein the travel of anindividual spring-biased tooth or the total travel of two diametricallyopposed spring-biased teeth is from about 0.6 to about 0.8 millimeter.10. A hub as claimed in claim: 1, wherein at least two movable teeth areprovided on a common support spring-biased against the ring member. 11.A magnetic tape cassette, especially a compact cassette, having at leastone hub, for use with a tape transport apparatus having a drive spindleprovided with projecting keys, said hub being displaceable in saidcassette in at least the radial direction, and said hub comprising aring member on whose inner periphery there are arranged teeth fordriving engagement by said projecting keys on the drive spindle,whereinsaid teeth include, in circumferentially spaced relationship, aplurality of immovable teeth which are radially spaced from the spindle,and also, in the same plane with said immovable teeth, at least onemovable tooth which is spring-biased against the ring member to exertradial pressure on the drive spindle, so as to resiliently couple saidhub to said spindle and thereby counteract abrupt displacements of thehub relatively to the cassette and hence reduce correspondingfluctuations in pitch during the operation of the cassette.
 12. Amagnetic tape cassette as claimed in claim 11 wherein said at least onespring-biased tooth has a spring rate of from about 1 P/mm to 40 P/mm.